Magnetic resonance imaging apparatus and magnetic resonance imaging method

ABSTRACT

A magnetic resonance imaging apparatus according to the present embodiment includes sequence control circuitry. The sequence control circuitry collect first MR data in a first cardiac cycle by excitation of a first region including a first slice, and collects reference data used for phase correction of second MR data on a second slice not included in the first region before and after the collection of the first MR data in the first cardiac cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2017-199505, filed Oct. 13,2017, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate to a magnetic resonance imagingapparatus and a magnetic resonance imaging method.

BACKGROUND

A magnetic resonance imaging (hereinafter referred to as MRI) apparatuscollects image data in response to the first R wave, and then collectsreference data in response to the second R wave when performing imagingby a phase sensitive inversion recovery (hereinafter referred to asPSIR) method. Reference data is corrected after longitudinalmagnetization after collection of MR data has approximately recovered toregain the thermal equilibrium state. The MRI apparatus corrects thephase of the MR data by using the reference data, and generates a realimage. The PSIR method is often used when the heart of the subject isimaged, and thus adopts breath-holding imaging.

The imaging procedure of a conventional PSIR method requires datacollection over two heartbeats to obtain one real image, and has aproblem that the imaging time is long. An increase in the imaging timeleads to an increase in the breath-holding time, and an increase in thenumber of breath holds; therefore, there is concern regarding anincrease in the stress on the subject, and an effect on the imagequality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of the magnetic resonanceimaging apparatus according to the first embodiment.

FIG. 2 is a diagram showing an example of the sequences of the PSIRmethod executed in the first embodiment.

FIG. 3 is a diagram showing an example of the steps of the operation inthe first embodiment.

FIG. 4 is a diagram showing an example of the region to which variouspulses and various sequences in the first sequence and second sequenceare applied in the first embodiment.

FIG. 5 is a diagram showing an example of the slices on which multibandimaging is performed in the first collection sequence and the secondreference collection sequence in the application of the firstembodiment.

FIG. 6 is a diagram showing an example of the sequences of the PSIRmethod performed in the second embodiment.

FIG. 7 is a diagram showing an example of the steps of the operation inthe second embodiment.

FIG. 8 is a diagram showing an example of the sequences of the PSIRmethod performed in the third embodiment.

FIG. 9 is a diagram showing an example of the steps of the operation inthe third embodiment.

DETAILED DESCRIPTION

A magnetic resonance imaging apparatus according to the presentembodiment includes sequence control circuitry. The sequence controlcircuitry collects first MR data in a first cardiac cycle by excitationof a first region including a first slice, and collects reference dataused for phase correction of second MR data on a second slice notincluded in the first region before and after collection of the first MRdata in the first cardiac cycle.

A purpose is to reduce the imaging time in imaging by the PSIR method.

Hereinafter, a magnetic resonance imaging apparatus according to theembodiments will be described with reference to the accompanyingdrawings. In the following description, structural elements havingapproximately the same function and configuration will be assigned withthe same reference symbol, and repetitive descriptions will be givenonly where necessary.

First Embodiment

The general configuration of an MRI apparatus 100 in the presentembodiment will be described with reference to FIG. 1. FIG. 1 is adiagram showing a configuration of the MRI apparatus 100 in the presentembodiment. As shown in FIG. 1, the MRI apparatus 100 includes a staticmagnetic field magnet 101, a gradient coil 103, a gradient magneticfield power supply 105, a bed 107, bed control circuitry 109,transmission circuitry (transmitter) 113, a transmitter coil 115, areceiver coil 117, reception circuitry (receiver) 119, sequence controlcircuitry (sequence controller) 121, a bus 123, an interface (inputsection) 125, a display 127, a storage apparatus (memory) 129, andprocessing circuitry (processor) 131. The MRI apparatus 100 may includea hollow cylindrical shim coil between the static magnetic field magnet101 and the gradient coil 103.

The static magnetic field magnet 101 is a hollowapproximately-cylindrical magnet. The static magnetic field magnet 101is not necessarily approximately-cylindrical, and may be of an opentype. The static magnetic field magnet 101 generates a uniform staticmagnetic field in the inner space. For example, a superconducting magnetor the like is used as the static magnetic field magnet 101.

The gradient coil 103 is a hollow cylindrical coil. The gradient coil103 is provided inside the static magnetic field magnet 101. Thegradient coil 103 is a combination of three coils corresponding to X, Y,and Z-axes orthogonal to one another. The Z-axis direction is the samedirection as the direction of the static magnetic field. The Y-axisdirection is the vertical direction, and the X-axis direction isperpendicular to the Z-axis and the Y-axis. The three coils in thegradient coil 103 are individually supplied with a current from thegradient magnetic field power supply 105, and generate gradient magneticfields whose magnetic field intensity changes along the respective X, Y,and Z-axes.

The gradient magnetic fields of the X, Y, and Z-axes generated by thegradient coil 103 form, for example, a slice selection gradient magneticfield, a phase encoding gradient magnetic field, and a frequencyencoding gradient magnetic field (also referred to as a readout gradientmagnetic field). The slice selection gradient magnetic field is used todetermine an imaging slice. The phase encoding gradient magnetic fieldis used to change the phase of a magnetic resonance (hereinafterreferred to as MR) signal in accordance with the spatial position. Thefrequency encoding gradient magnetic field is used to change thefrequency of an MR signal in accordance with the spatial position.

The gradient magnetic field power supply 105 is a power supply devicethat supplies a current to the gradient coil 103 under the control ofthe sequence control circuitry 121.

The bed 107 is an apparatus including a top plate 1071 on which thesubject P is placed. The bed 107 inserts the top plate 1071 on which thesubject P is placed into a bore 111 under the control of the bed controlcircuitry 109. The bed 107 is installed in an examination room in whichthe present MRI apparatus 100 is installed in such a manner that, forexample, its longitudinal direction is parallel to the central axis ofthe static magnetic field magnet 101.

The bed control circuitry 109 is circuitry that controls the bed 107,and drives the bed 107 in response to an operator's instruction via theinterface 125 to move the top plate 1071 in the longitudinal directionand vertical direction.

The transmission circuitry 113 supplies a radio frequency pulse (RFpulse) corresponding to the Larmor frequency or the like to thetransmitter coil 115 under the control of the sequence control circuitry121.

The transmitter coil 115 is an RF coil provided inside the gradient coil103. The transmitter coil 115 is supplied with the RF pulse from thetransmission circuitry 113 and generates a transmit RF wavecorresponding to a radio frequency magnetic field. The transmitter coil115 is, for example, a whole body coil (WB coil). The WB coil may beused as a transmitter/receiver coil.

The receiver coil 117 is an RF coil provided inside the gradient coil103. The receiver coil 117 receives an MR signal that the radiofrequency magnetic field causes the subject P to emit. The receiver coil117 outputs the received MR signal to the reception circuitry 119. Thereceiver coil 117 is, for example, a coil array that has one or more,and typically a plurality of coil elements. FIG. 1 shows the transmittercoil 115 and the receiver coil 117 as separate RF coils; however, thetransmitter coil 115 and the receiver coil 117 may be embodied as anintegrated transmitter/receiver coil. The transmitter/receiver coilcorresponds to the imaging target of the subject P, and is a localtransmitter/receiver RF coil such as a head coil.

The reception circuitry 119 generates a digital MR signal that isdigitized complex data, based on the MR signal output from the receivercoil 117, under the control of the sequence control circuitry 121.Specifically, the reception circuitry 119 performs various types ofsignal processing on the MR signal output from the receiver coil 117,and then performs analog-to-digital (A/D) conversion on the datasubjected to the various types of signal processing. The receptioncircuitry 119 samples the A/D-converted data. The reception circuitry119 thereby generates a digital MR signal (hereinafter referred to as MRdata). The reception circuitry 119 outputs the generated MR data to thesequence control circuitry 121.

In accordance with an imaging protocol output from the processingcircuitry 131, the sequence control circuitry 121 controls, for example,the gradient magnetic field power supply 105, the transmission circuitry113, and the reception circuitry 119, and performs imaging on thesubject P. The imaging protocol includes various pulse sequencescorresponding to the examination. The imaging protocol defines themagnitude of the current supplied from the gradient magnetic field powersupply 105 to the gradient coil 103, timing of the supply of the currentfrom the gradient magnetic field power supply 105 to the gradient coil103, the magnitude of the RF pulse supplied from the transmissioncircuitry 113 to the transmitter coil 115, timing of the supply of theRF pulse from the transmission circuitry 113 to the transmitter coil115, and timing of reception of the MR signal at the receiver coil 117,etc.

The bus 123 is a transmission path for transmitting data between theinterface 125, the display 127, the storage apparatus 129, and theprocessing circuitry 131. The bus 123 may be connected via, for example,a network to various physiological signal measuring devices, an externalstorage apparatus, and various modalities. For example, anelectrocardiograph (not shown) is connected to the bus as aphysiological signal measuring device.

The interface 125 includes a circuit that receives various instructionsand information inputs from the operator. The interface 125 includes acircuit relating to, for example, a pointing device such as a mouse, oran input device such as a keyboard. The circuit included in theinterface 125 is not limited to a circuit relating to a physicaloperational component, such as a mouse or a keyboard. For example, theinterface 125 may include an electrical signal processing circuit thatreceives an electrical signal corresponding to an input operation froman external input device provided separately from the present MRIapparatus 100 and outputs the received electrical signal to variouscircuits.

The display 127 displays, for example, various MR images generated by animage generation function, and various types of information on imagingand image processing, under the control of a system control function1311 in the processing circuitry 131. The display 127 is, for example, adisplay device, such as a CRT display, a liquid crystal display, anorganic EL display, an LED display, a plasma display, or any otherdisplay or monitor known in the relevant technical field.

The storage apparatus 129 stores, for example, MR data filled in the kspace via the image generation function 1313, and image data generatedby the image generation function 1313. The storage apparatus 129 stores,for example, various imaging protocols, and an imaging conditionincluding a plurality of imaging parameters defining each imagingprotocol. The storage apparatus 129 stores programs corresponding tovarious functions performed by the processing circuitry 131. The storageapparatus 129 is, for example, a semiconductor memory element, such as arandom access memory (RAM) or a flash memory, a hard disk drive, a solidstate drive, or an optical disk. The storage apparatus 129 may also be,for example, a drive that performs writing and reading of various typesof information on a CD-ROM drive, a DVD drive, or a portable memorymedium such as a flash memory.

The processing circuitry 131 includes, as hardware resources, aprocessor and a memory such as a read-only memory (ROM) and a RAM, whichare not shown, and collectively controls the present MRI apparatus 100.The processing circuitry 131 has a system control function 1311, and animage generation function 1313. Various functions performed by thesystem control function 1311, and the image generation function 1313,are stored in the storage apparatus 129 in the form of a programexecutable by a computer. The processing circuitry 131 is a processorthat reads programs corresponding to the various functions from thestorage apparatus 129 and executes them to realize functionscorresponding to the programs. In other words, the processing circuitry131 that has read the programs has, for example, the functions shown inthe processing circuitry 131 in FIG. 1.

FIG. 1 illustrates the case where the various functions are realized ina single processing circuit 131; however, the processing circuitry 131may be constituted by a combination of a plurality of independentprocessors, and the functions may be realized by the processorsexecuting the programs. In other words, the above-described functionsmay be configured as programs and executed by a single processingcircuit; alternatively, a specific function may be implemented in adedicated independent program execution circuit. The system controlfunction 1311 and image generation function 1313 of the processingcircuitry 131 are examples of a system controller and an imagegeneration section, respectively.

The term “processor” used in the above description means, for example, acircuit such as a central processing unit (CPU), a graphics processingunit (GPU), an application specific integrated circuit (ASIC), or aprogrammable logic device (e.g., a simple programmable logic device(SPLD), a complex programmable logic device (CPLD), or a fieldprogrammable gate array (FPGA)).

The processor realizes various functions by reading and executingprograms stored in the storage apparatus 129. The programs may bedirectly integrated in a circuit of the processor, instead of beingstored in the storage apparatus 129. In this case, the processorrealizes functions by reading and executing programs integrated in thecircuit. Similarly, the bed control circuitry 109, the transmissioncircuitry 113, the reception circuitry 119, and the sequence controlcircuitry 121, etc. are constituted by an electronic circuit such as theabove-described processor.

The processing circuitry 131 controls the MRI apparatus 100 by thesystem control function 1311. Specifically, the processing circuitry 131reads the system control program stored in the storage apparatus 129,loads it in the memory, and controls each circuitry of the present MRIapparatus 100 in accordance with the loaded system control program. Forexample, the processing circuitry 131 reads an imaging protocol from thestorage apparatus 129 by the system control function 1311 based on animaging condition input by the operator via the interface 125. Theprocessing circuitry 131 may generate the imaging protocol based on theimaging condition. The processing circuitry 131 transmits the imagingprotocol to the sequence control circuitry 121, and controls imaging onthe subject P.

With the image generation function 1313, the processing circuitry 131fills MR data in the readout direction of the k space in accordance withthe intensity of the readout gradient magnetic field. The processingcircuitry 131 performs the Fourier transform on the MR data filled inthe k space to generate an MR image. For example, the processingcircuitry 131 can generate a magnitude image from complex MR data. Theprocessing circuitry 131 can also generate a phase image by using realpart data and imaginary part data of the complex MR data. The processingcircuitry 131 outputs an MR image such as a magnitude image or phaseimage to the display 127 and the storage apparatus 129.

This is the description of the overall configuration of the MRIapparatus 100 according to the present embodiment. Hereinafter,sequences executed in the present MRI apparatus 100 will be described.To specifically describe the PSIR method in the present embodiment, letus assume that the imaging target site on which the sequences executedby the present MRI apparatus 100 are applied is a heart to which acontrast medium has been given. The PSIR method is a delayed enhancedMRI that does not require setting of the inversion time (TI). The PSIRmethod is an imaging sequence for obtaining an image in which adifference (T1 contrast) between the longitudinal relaxation time ofnormal myocardium and that of an impaired myocardium is enhanced in aheart to which a contrast medium was given in advance. The impairment ofthe myocardium is, for example, an infarction. The imaging target siteto which the sequences executed by the present MRI apparatus 100 areapplied is not limited to the heart, and may be other imaging targetsites. The sequence control circuitry 121 executes a first sequence in afirst cardiac cycle of two adjacent cardiac cycles, and executes asecond sequence in a second cardiac cycle that follows the first cardiaccycle. The imaging protocol including the first sequence and the secondsequence is stored in the storage apparatus 129. The first sequence andthe second sequence will be described in detail later.

FIG. 2 is a diagram showing an example of the sequences of the PSIRmethod executed in the present embodiment. (a) in FIG. 2 shows awaveform of an electrocardiogram (ECG) of the subject P obtained by anelectrocardiograph (hereinafter referred to as an electrocardiographicwaveform). CC1 in (a) of FIG. 2 indicates the first cardiac cyclebetween two adjacent R waves. CC2 in (a) of FIG. 2 indicates the secondcardiac cycle that follows the first cardiac cycle CC1. The sequencecontrol circuitry 121 executes a first sequence S1 in the first cardiaccycle CC1, and executes a second sequence S2 in the second cardiaccycle.

(b) in FIG. 2 indicates the timing of application of an inversionrecovery pulse (hereinafter referred to as an IR pulse) to the subjectP. The IR pulse is a pulse that inverts nuclear magnetization in theregion to which the IR pulse is applied. The timing of application ofthe IR pulse is set, for example, as follows: First, a period from whenlongitudinal magnetization of a normal myocardium is inverted by an IRpulse to when longitudinal magnetization of the normal myocardiumbecomes zero (hereinafter referred to as a recovery period) is set.Then, a time phase of the cardiac cycle at a point in time that is therecovery period before the starting time of the diastolic phase(hereinafter referred to as a specific time phase) is identified. Thetime from an R wave to the specific time phase in one cardiac cycle(hereinafter referred to as a predetermined time) is determined. Thepredetermined time is stored in the storage apparatus 129. The timing ofapplication of the IR pulse is set to the predetermined time after an Rwave in each of a plurality of cardiac cycles.

(c) in FIG. 2 shows a temporal change of longitudinal magnetization Mz1in a first slice.

(d) in FIG. 2 shows a temporal change of longitudinal magnetization Mz2in a second slice apart from a first region including the first sliceand thicker than the first slice. For example, when the heart of thesubject P is divided into two regions, i.e., a region including acardiac base and a region including a cardiac apex, the first regioncorresponds to, for example, the region including the cardiac base. Theregion including the cardiac apex corresponds to a second regionincluding the second slice and thicker than the second slice.

Hereinafter, the first sequence S1 executed by the sequence controlcircuitry 121 in the first cardiac cycle CC1 will be described. Thefirst sequence S1 includes a first IR pulse IR1, a first collectionsequence M1, a first spoiler pulse Sp1, and a second referencecollection sequence R2.

The first IR pulse IR1 is an RF pulse that inverts nuclear magnetizationin the first region. The first IR pulse IR1 is applied to the firstregion at time t₁, which is the predetermined time after an R wave inthe first cardiac cycle CC1.

The first collection sequence M1 is a sequence for collecting MR datafor an image relating to the first slice (hereinafter referred to asfirst MR data) after application of the first IR pulse IR1 in the firstcardiac cycle CC1. As a sequence executed in the first collectionsequence M1, for example, a gradient echo that performs imaging with ashort repetition time (TR) and a small flip angle is used. The gradientecho is for example, a 2D segmented fast low angle shot (FLASH).

The first spoiler pulse Sp1 is a spoiler pulse that recovers nuclearmagnetization in the first region. After execution of the firstcollection sequence M1 in the first cardiac cycle CC1, the first spoilerpulse Sp1 is applied to the first region. The first spoiler pulse Sp1is, for example, a gradient magnetic field spoiler for gradientspoiling. The first spoiler pulse Sp1 is not limited to the gradientmagnetic field spoiler, and may be, for example, an RF pulse thatforcibly recovers longitudinal magnetization Mz (hereinafter referred toas an RF spoiler). Alternatively, both a gradient magnetic field spoilerand RF spoiler may be used as the first spoiler pulse Sp1.

The second reference collection sequence R2 is a sequence for collectingreference data in the second slice (hereinafter referred to as secondreference data) after application of the first spoiler pulse Sp1 in thefirst cardiac cycle CC1. The second reference data is used for phasecorrection of MR data for an image corrected by the second collectionsequence M2 to be described later (hereinafter referred to as second MRdata) and the second reference data. The phase correction will bedescribed in detail later. The second reference collection sequence R2is the same as the first collection sequence M1 other than the flipangle, which is smaller than that in the first collection sequence M1,the collection timing, and the slice position.

Hereinafter, the second sequence S2 executed by the sequence controlcircuitry 121 in the second cardiac cycle CC2 will be described. Thesecond sequence S2 includes a second IR pulse IR2, a second collectionsequence M2, a second spoiler pulse Sp2, and a first referencecollection sequence R1.

The second IR pulse IR2 is an RF pulse that inverts nuclearmagnetization in the second region. The second IR pulse IR2 is appliedto the second region at time t₂, which is the predetermined time afteran R wave in the second cardiac cycle CC2.

The second collection sequence. M2 is a sequence for collecting secondMR data on the second slice after application of the second IR pulse IR2in the second cardiac cycle CC2. The second collection sequence M2 isthe same as the first collection sequence M1 other than the cardiaccycle and the slice position.

The second spoiler pulse Sp2 is a spoiler pulse that recovers nuclearmagnetization in the second region. After execution of the secondcollection sequence M2 in the second cardiac cycle CC2, the secondspoiler pulse Sp2 is applied to the second region. The second spoilerpulse Sp2 is the same as the first spoiler pulse Sp1 other than thecardiac cycle and the application region.

The first reference collection sequence R1 is a sequence for collectingreference data from the first slice (hereinafter referred to as firstreference data) after application of the second spoiler pulse Sp2 in thesecond cardiac cycle CC2. The first reference data is used for phasecorrection of the first MR data and the first reference data. The firstreference collection sequence R1 is the same as the second referencecollection sequence R2 other than the cardiac cycle and the sliceposition.

(Operation)

The steps of the operation in the present embodiment will be describedwith reference to FIGS. 3 and 4. FIG. 3 is a diagram showing an exampleof the steps of the operation in the present embodiment. FIG. 4 is adiagram showing an example of the region to which various pulses andvarious sequences in the first sequence S1 and second sequence S2 areapplied. In (a) of FIG. 4, the first region Re1 to which the first IRpulse IR1 is applied is indicated by hatching. (b) in FIG. 4 shows thefirst slice SL1 from which the first MR data is collected, and thesecond slice SL2 from which the second reference data is collected. In(c) of FIG. 4, the second region Re2 to which the second IR pulse IR2 isapplied is indicated by hatching. (d) in FIG. 4 shows the first sliceSL1 from which the first reference data is collected, and the secondslice SL2 from which the second MR data is collected.

(Step Sa1)

The sequence control circuitry 121 executes the first sequence S1 tocollect first MR data and second reference data in the first cardiaccycle CC1. Specifically, as shown in FIGS. 2 and 4, the sequence controlcircuitry 121 controls the transmission circuitry 113 to apply the firstIR pulse IR1 to the first region Re1 at time t₁, which is thepredetermined time after the detection time (t₀) of the first R wave inthe first cardiac cycle CC1. As shown in (a) of FIG. 4, the first IRpulse IR1 is not a non-selective IR pulse, but a selective IR pulse thatis selectively applied to the first slice SL1. As shown in (a) of FIG.4, the first region Re1 is thicker than the first slice SL1 to be imagedat the imaging target site.

As shown in FIGS. 2 and 4, the sequence control circuitry 121 executesthe first collection sequence M1 in an approximate diastolic phase ofthe first cardiac cycle CC1, and collects first MR data on the firstslice SL1. After collection of the first MR data, the sequence controlcircuitry 121 controls the transmission circuitry 113 and/or thegradient magnetic field power supply 105 to apply the first spoilerpulse Sp1 to the first region Re1. After application of the firstspoiler pulse Sp1, the sequence control circuitry 121 executes thesecond reference collection sequence R2, and collects second referencedata on the second slice SL2. The sequence control circuitry 121 outputsthe first MR data and the second reference data to the processingcircuitry 131.

(Step Sa2)

The sequence control circuitry 121 executes the second sequence S2 tocollect second MR data and first reference data in the second cardiaccycle CC2. Specifically, as shown in FIGS. 2 and 4, the sequence controlcircuitry 121 controls the transmission circuitry 113 to apply thesecond IR pulse IR2 to the second region Re2 at time t₂, which is thepredetermined time after the detection time of the first R wave in thesecond cardiac cycle CC2 (or the last R wave in the first cardiac cycleCC1). Like the first IR pulse IR1, the second IR pulse IR2 is not anon-selective IR pulse, but a selective pulse that is selectivelyapplied to the second slice SL2, as shown in (c) of FIG. 4. As shown in(c) of FIG. 4, the second region Re2 is thicker than the second sliceSL2 to be imaged at the imaging target site.

As shown in (d) of FIG. 2 and (d) of FIG. 4, the sequence controlcircuitry 121 executes the second collection sequence M2 in anapproximate diastolic phase of the second cardiac cycle CC2, andcollects second MR data on the second slice SL2. After collection of thesecond MR data, the sequence control circuitry 121 controls thetransmission circuitry 113 and/or the gradient magnetic field powersupply 105 to apply the second spoiler pulse Sp2 to the second regionRe2. After application of the second spoiler pulse Sp2, the sequencecontrol circuitry 121 executes the first reference collection sequenceR1, and collects first reference data on the first slice SL1. Thesequence control circuitry 121 outputs the second MR data and the firstreference data to the processing circuitry 131.

(Step Sa3)

With the image generation function 1313, the processing circuitry 131generates first phase correction data based on the first reference data.The processing circuitry 131 generates second phase correction databased on the second reference data. The first phase correction datacorresponds to a weight for canceling a phase distortion (phase error)caused by, for example, the transmitter coil 117 regarding the firstslice SL1. The second phase correction data corresponds to a weight forcanceling a phase distortion (phase error) caused by, for example, thetransmitter coil 117 regarding the second slice SL2. Specifically, theprocessing circuitry 131 generates the first phase correction data byusing the first reference data, the complex conjugate of the firstreference data, and noise variance measured in advance. The processingcircuitry 131 generates the second phase correction data by using thesecond reference data, the complex conjugate of the second referencedata, and the aforementioned noise variance.

(Step Sa4)

With the image generation function 1313, the processing circuitry 131performs phase correction on each of the first MR data and the firstreference data by using the first phase correction data. The processingcircuitry 131 performs phase correction on each of the second MR dataand the second reference data by using the second phase correction data.The phase correction in the processing of this step cancels the phaseerror in each of the first MR data, the second MR data, the firstreference data, and the second reference data.

(Step Sa5)

With the image generation function 1313, the processing circuitry 131removes phase information from the phase-corrected first MR data byusing the phase-corrected first reference data. The processing circuitry131 removes phase information from the phase-corrected second MR data byusing the phase-corrected second reference data. Specifically, theprocessing circuitry 131 calculates first phase information by using thereal component and imaginary component of the phase-corrected firstreference data. Then, the processing circuitry 131 removes the firstphase information from the phase-corrected first MR data. The polarityof the signal of the first MR data is maintained in the real componentof data obtained by removing the first phase information from thephase-corrected first MR data (hereinafter referred to as firstphase-removed data). The processing circuitry 131 calculates secondphase information by using the real component and imaginary component ofthe phase-corrected second reference data. Then, the processingcircuitry 131 removes the second phase information from thephase-corrected second MR data. The polarity of the signal of the secondMR data is maintained in the real component of data obtained by removingthe second phase information from the phase-corrected second MR data(hereinafter referred to as second phase-removed data).

(Step Sa6)

With the image generation function 1313, the processing circuitry 131reconstructs a first real image by using the real component of the firstphase-removed data. The processing circuitry 131 reconstructs a secondreal image by using the real component of the second phase-removed data.In this step, the processing circuitry 131 may perform correction toaddress uneven sensitivity of the receiver coil 117 on the first realimage and the second real image by using a sensitivity map of thereceiver coil 117.

The processing circuitry 131 outputs the first real image and the secondreal image to, for example, the display 127 and the storage apparatus129. The display 127 displays the first real image and the second realimage. The storage apparatus 129 stores the first real image and thesecond real image. The processing from step Sa1 to step Sa6 may berepeated as appropriate. The processing from step Sa1 to step Sa6 may berepeated as appropriate until a plurality of real images correspondingto a plurality of slices required by the operator can be obtained at theimaging target site.

The above-described configuration has the following advantages:

The MRI apparatus 100 according to the present embodiment can execute,in a first cardiac cycle CC1, a first sequence S1 for applying a firstIR pulse IR1 to a first region Re1 that includes a first slice SL1 andis thicker than the first slice SL1, collecting first MR data on thefirst slice SL1 after application of the first IR pulse IR1, applying afirst spoiler pulse Sp1 for recovery of nuclear magnetization to thefirst region Re1 after collection of the first MR data, and collectingsecond reference data for second MR data on a second slice SL2 apartfrom the first region Re1 after application of the first spoiler pulseSp1. The present MRI apparatus 100 can also execute, in a second cardiaccycle CC2, a second sequence S2 for applying a second IR pulse IR2 to asecond region Re2 that includes the second slice SL2 and is thicker thanthe second slice SL2, collecting the second MR data after application ofthe second IR pulse IR2 on the second region Re2, applying a secondspoiler pulse Sp2 to the second region Re2 after collection of thesecond MR data, and collecting first reference data for the first MRdata after application of the second spoiler pulse Sp2.

As described above, the MRI apparatus 100 in the present embodiment canreduce the imaging time in imaging by the PSIR method. In addition, thepresent MRI apparatus 100 can apply the first IR pulse IR1 to the firstregion Re1, and apply the second IR pulse IR2 to the second region Re2,and thus can reliably apply IR pulses to the slices to be imaged.Therefore, when the imaging target site moves in the subject P duringimaging, the present MRI apparatus 100 can avoid extension of theimaging time caused by a deviation of the application position of an IRpulse, in comparison to the case where an IR pulse is selectivelyapplied to a slice to be imaged.

(Application)

The application differs from the first embodiment in that multi-slicesimultaneous imaging (hereinafter referred to as multiband imaging) isperformed in the first and second collection sequences M1 and M2, andthe first and second reference collection sequences R1 and R2.Hereinafter, the multiband imaging will be described with reference toFIG. 5. FIG. 5 is a diagram showing an example of the slices on whichmultiband imaging is performed in the first collection sequence M1, andthe second reference collection sequence R2.

In (a) of FIG. 5, the first region Re1 to which the first IR pulse IR1is applied is indicated by hatching. (b) in FIG. 5 shows a plurality ofslices SL1-1 and SL1-2 included in the first slice SL1 from which firstMR data is collected, and a plurality of slices SL2-1 and SL2-2 includedin the second slice SL2 from which second reference data is collected.

Hereinafter, to provide specific descriptions, let us assume that thefirst region Re1 and the second region Re2 each include four slices asshown in FIG. 5. Let us also assume that the first slice SL1 and thesecond slice SL2 each have a thickness corresponding to two slices. Thenumber of slices included in each of the first slice SL1 and the secondslice SL2 is not limited to two as shown in FIG. 5, and may be three orlarger. The number of slices included in each of the first region Re1and the second region Re2 is not limited to four, and may be larger.

The sequence control circuitry 121 sets the thicknesses of the first andsecond slices SL1 and SL2 on which multiband imaging is performed, forexample, in accordance with the operator's instructions via theinterface 125. The set thicknesses are those including a plurality ofslices SL1-1 and SL1-2, and SL2-1 and SL2-2. The thicknesses formultiband imaging may be stored in the storage apparatus 129 inassociation with the first and second sequences S1 and S2.

The sequence control circuitry 121 determines multi-frequency bands ofRF pulses used in the first and second collection sequences M1 and M2and the first and second reference collection sequences R1 and R2, basedon the set thicknesses each corresponding to a plurality of slices, thepositions of a plurality of slices in the bore 111, and the sliceselection gradient magnetic field. The multi-frequency bands of RFpulses for multiband imaging may be stored in the storage apparatus 129in association with the first and second sequences S1 and S2 by default.

The sequence control circuitry 121 executes the first collectionsequence M1 to apply an RF pulse in a multi-frequency band to a firstslice SL1 including slice SL1-1 and slice SL1-2. The sequence controlcircuitry 121 executes the second reference collection sequence R2 toapply an RF pulse in a multi-frequency band to a second slice SL2including slice SL2-1 and slice SL2-2.

The sequence control circuitry 121 executes the second collectionsequence M2 to apply an RF pulse in a multi-frequency band to the secondslice SL2 including slice SL2-1 and slice SL2-2. The sequence controlcircuitry 121 executes the first reference collection sequence R1 toapply an RF pulse in a multi-frequency band to the first slice SL1including slice SL1-1 and slice SL1-2.

With the image generation function 1313, the processing circuitry 131divides the first MR data into MR data corresponding to slice SL1-1 andMR data corresponding to slice SL1-2 by using the sensitivity map of thereceiver coil 117. The processing circuitry 131 divides the secondreference data into reference data corresponding to slice SL2-1 andreference data corresponding to slice SL2-2 by using the sensitivity mapof the receiver coil 117. The processing circuitry 131 divides thesecond MR data into MR data corresponding to slice SL2-1 and MR datacorresponding to slice SL2-2 by using the sensitivity map of thereceiver coil 117. The processing circuitry 131 divides the firstreference data into reference data corresponding to slice SL1-1 andreference data corresponding to slice SL1-2 by using the sensitivity mapof the receiver coil 117. The processing circuitry 131 performs theprocessing from step Sa3 to step Sa6 in FIG. 3 on each of slice SL1-1,slice SL1-2, slice SL2-2, and slice SL2-2, and generates a real image ofeach of slice SL1-1, slice SL1-2, slice SL2-2, and slice SL2-2.

The above-described configuration has the following advantages inaddition to the advantages of the first embodiment:

According to the MRI apparatus 100 according to this application, thefirst slice SL1 has a thickness corresponding to a plurality of slices,the second slice SL2 has a thickness corresponding to a plurality ofslices, an RF pulse in a multi-frequency band corresponding to the firstslice SL1 can be applied to the first slice SL1 when first MR data iscollected, and when first reference data is collected, an RF pulse in amulti-frequency band corresponding to the second slice SL2 can beapplied to the second slice SL2 when second MR data is collected andwhen second reference data is collected. Accordingly, the MRI apparatus100 in this application can simultaneously image multiple slices inimaging by the PSIR method, and can further reduce the imaging time incomparison with the MRI apparatus in the first embodiment.

Second Embodiment

The second embodiment differs from the first embodiment and theapplication in that second reference data is further collected from thesecond slice SL2 immediately before collection of the first MR data inthe first cardiac cycle CC1, and first reference data is furthercollected from the first slice SL1 immediately before collection of thesecond MR data in the second cardiac cycle CC2. The second embodimentfurther differs from the first embodiment and the application in thatthe first IR pulse IR1 and the first spoiler pulse Sp1 are selectivelyapplied to the first slice SL1, and the second IR pulse IR2 and thesecond spoiler pulse Sp2 are selectively applied to the second sliceSL2.

For example, the sequence control circuitry 121 applies the first IRpulse IR1 and the first spoiler pulse Sp1 to the first region Re1 with agradient magnetic field that selects the first region Re1 including thefirst slice SL1. The sequence control circuitry 121 also applies thesecond IR pulse IR2 and the second spoiler pulse Sp2 to the secondregion Re2 with a gradient magnetic field that selects the second regionRe2 including the second slice SL2.

FIG. 6 is a diagram showing an example of the sequences of the PSIRmethod executed in the present embodiment. (a) in FIG. 6 shows anelectrocardiographic waveform of the subject P obtained by anelectrocardiograph. (b) in FIG. 6 shows the timing of application of thefirst IR pulse IR1 and the second IR pulse IR2 to the subject P. (c) inFIG. 6 shows a temporal change of longitudinal magnetization Mz1 in thefirst slice SL1. (d) in FIG. 6 shows a temporal change of longitudinalmagnetization Mz2 in the second slice SL2.

As shown in FIG. 6, the first sequence S1 further includes a referencecollection sequence R2-1 for collecting second reference data from thesecond slice SL2 immediately before collection of the first MR data. Asshown in FIG. 6, the second sequence S2 further includes a referencecollection sequence R1-1 for collecting first reference data from thefirst slice SL1 immediately before collection of the second MR data. Thereference collection sequence R2-2 in the present embodiment correspondsto the second reference collection sequence R2 in the first embodiment.The reference collection sequence R1-2 in the present embodimentcorresponds to the first reference collection sequence R1 in the firstembodiment.

The reference collection sequence R2-2 differs from the referencecollection sequence R2-1 in terms of the collection timing in the firstcardiac cycle CC1. The starting time of the reference collectionsequence R2-1 in the first sequence 81 is a cardiac phase at a time theexecution period of the reference collection sequence R2-2 before thestarting time of the first collection sequence M1, and is associatedwith the first R wave in the first cardiac cycle CC1. The starting timeof the reference collection sequence R2-1 is stored in the storageapparatus 129 together with the first sequence S1.

The reference collection sequence R1-2 differs from the referencecollection sequence R1-1 in terms of the collection timing in the secondcardiac cycle CC2. The starting time of the reference collectionsequence R1-1 in the second sequence S2 is a cardiac phase at a time theexecution period of the reference collection sequence R1-2 before thestarting time of the second collection sequence M2, and is associatedwith the first R wave in the second cardiac cycle CC2. The starting timeof the reference collection sequence R1-1 is stored in the storageapparatus 129 together with the second sequence S2.

(Operation)

The steps of the operation in the present embodiment will be describedwith reference to FIGS. 6 and 7. FIG. 7 is a diagram showing an exampleof the steps of the operation in the present embodiment. In thedescription of the operation, the processing different from that in thefirst embodiment will be described.

(Step Sb1)

The sequence control circuitry 121 executes the first sequence S1 tocollect first MR data and two kinds of second reference data in thefirst cardiac cycle CC1. For example, the sequence control circuitry 121collects first MR data in the first cardiac cycle CC1 by excitation ofthe first region Re1 including the first slice SL1, and collectsreference data (second reference data) used for phase correction ofsecond MR data on the second slice SL2 not included in the first regionRe1 before and after collection of the first MR data in the same firstcardiac cycle CC1. Specifically, as shown in (b) of FIG. 6, the sequencecontrol circuitry 121 controls the transmission circuitry 113 to applythe first IR pulse IR1 to the first slice SL1 at time t₁, in response tothe first R wave in the first cardiac cycle CC1. The first IR pulse IR1in the present embodiment is a selective IR pulse that is selectivelyapplied to the first slice SL1.

The sequence control circuitry 121 executes the reference collectionsequence R2-1 in response to the R wave to collect first-secondreference data in the first cardiac cycle CC1. The sequence controlcircuitry 121 collects first MR data after collection of thefirst-second reference data. To apply the first spoiler pulse Sp1 to thefirst slice SL1 after collection of the first MR data, the sequencecontrol circuitry 121 controls the transmission circuitry 113 and/or thegradient magnetic field power supply 105. The sequence control circuitry121 executes the reference collection sequence R2-2 after application ofthe first spoiler pulse Sp1 to collect second-second reference data. Thesequence control circuitry 121 outputs the two kinds of collected secondreference data to the processing circuitry 131.

(Step Sb2)

The sequence control circuitry 121 executes the second sequence S2 tocollect second MR data and two kinds of first reference data in thesecond cardiac cycle CC2. For example, the sequence control circuitry121 collects second MR data in the second cardiac cycle CC2 that isdifferent from the first cardiac cycle CC1 by excitation of the secondregion Re2 including the second slice SL2, and

-   -   Specifically, as shown in (b) of FIG. 6, the sequence control        circuitry 121 controls the transmission circuitry 113 to apply        the second IR pulse IR2 to the second slice SL2 at time t₂, in        response to the first R wave in the second cardiac cycle CC2 (or        the last R wave in the first cardiac cycle CC1). The second IR        pulse IR2 in the present embodiment is a selective IR pulse that        is selectively applied to the second slice SL2.

The sequence control circuitry 121 executes the reference collectionsequence R1-1 in response to the R wave to collect first-first referencedata in the second cardiac cycle CC2. The sequence control circuitry 121collects second MR data after collection of the first-first referencedata. To apply the second spoiler pulse Sp2 to the second slice SL2after collection of the second MR data, the sequence control circuitry121 controls the transmission circuitry 113 and/or the gradient magneticfield power supply 105. The sequence control circuitry 121 executes thereference collection sequence R1-2 after application of the secondspoiler pulse Sp2 to collect second-first reference data. The sequencecontrol circuitry 121 outputs the two kinds of collected first referencedata to the processing circuitry 131.

(Step Sb3)

With the image generation function 1313, the processing circuitry 131performs phase correction on the second MR data obtained in the secondcardiac cycle CC2 by using the second reference data. Specifically, withthe image generation function 1313, the processing circuitry 131calculates the average of the two kinds of first reference data on thefirst slice SL1 to generate first average data. The first average datais, for example, data obtained by averaging the phase components of thetwo kinds of first reference data. The first average data may begenerated by weighted-summing the intensity components of the two kindsof first reference data.

(Step Sb4)

With the image generation function 1313, the processing circuitry 131calculates the average of the two kinds of second reference data on thesecond slice SL2 to generate second average data. The second averagedata is, for example, data obtained by averaging the phase components ofthe two kinds of second reference data. The second average data may begenerated by weighted-summing the intensity components of the two kindsof second reference data.

(Step Sb5)

With the image generation function 1313, the processing circuitry 131generates first phase correction data based on the first average data.The processing circuitry 131 generates second phase correction databased on the second average data.

(Step Sb6)

With the image generation function 1313, the processing circuitry 131performs phase correction on each of the first MR data and the firstaverage data by using the first phase correction data. The processingcircuitry 131 performs phase correction on each of the second MR dataand the second average data by using the second phase correction data.The phase correction in the processing of this step cancels the phaseerror in each of the first MR data, the second MR data, the firstaverage data, and the second average data.

(Step Sb7)

With the image generation function 1313, the processing circuitry 131removes phase information from the phase-corrected first MR data byusing the phase-corrected first average data. The processing circuitry131 removes phase information from the phase-corrected second MR data byusing the phase-corrected second average data. Specifically, theprocessing circuitry 131 calculates first phase information by using thereal component and imaginary component of the phase-corrected firstaverage data. Then, the processing circuitry 131 removes the first phaseinformation from the phase-corrected first MR data. The processingcircuitry 131 calculates second phase information by using the realcomponent and imaginary component of the phase-corrected second averagedata. Then, the processing circuitry 131 removes the second phaseinformation from the phase-corrected second MR data. The subsequentprocessing is the same as the processing of step Sa6 in FIG. 3, anddescriptions thereof will be omitted. In the processing of step Sa6subsequent to this step Sb7, the processing circuitry 131 may performcorrection to address uneven sensitivity of the receiver coil 117 on thefirst real image and the second real image by using the sensitivity mapof the receiver coil 117. The processing from step Sb1 to step Sb7 andthe processing of step Sa6 subsequent to step Sb7 may be repeated asappropriate. The processing from step Sb1 to step Sb7 and the processingof step Sa6 subsequent to step Sb7 may be repeated as appropriate untila plurality of real images corresponding to a plurality of slicesrequired by the operator can be obtained at the imaging target site.

The above-described configuration has the following advantages:

The MRI apparatus 100 according to the present embodiment can execute,in a first cardiac cycle CC1, a first sequence S1 for applying a firstIR pulse IR1 to a first slice SL1, collecting second reference data fromthe second slice SL2 after application of the first IR pulse IR1 andimmediately before collection of first MR data, collecting the first MRdata, applying a first spoiler pulse Sp1 to the first slice SL1 aftercollection of the first MR data, and collecting again second referencedata from the second slice SL2 after application of the first spoilerpulse Sp1. The present MRI apparatus 100 can also execute, in a secondcardiac cycle CC2, a second sequence S2 for applying a second IR pulseIR2 to the second slice SL2, collecting first reference data from thefirst slice SL1 after application of the second IR pulse IR2 andimmediately before collection of second MR data, collecting the secondMR data, applying a second spoiler pulse Sp2 to the second slice SL2after collection of the second MR data, and collecting again firstreference data from the first slice SL1 after application of the secondspoiler pulse Sp2.

Moreover, the present MRI apparatus 100 can collect first MR data in thefirst cardiac cycle CC1 by excitation of a first region Re1 includingthe first slice SL1, and can collect reference data used for phasecorrection of second MR data on the second slice SL2 not included in thefirst region Re1 before and after collection of the first MR data in thesame first cardiac cycle CC1. Furthermore, the present MRI apparatus 100can collect second MR data in the second cardiac cycle CC2 that isdifferent from the first cardiac cycle CC1 by excitation of a secondregion Re2 including the second slice SL2, and can phase-correct thesecond MR data obtained in the second cardiac cycle CC2 by using thereference data.

As described above, the MRI apparatus 100 in the present embodiment canreduce the imaging time in imaging by the PSIR method. In addition, thepresent MRI apparatus 100 can phase-correct the first MR data by usingfirst average data near the time phase of the first collection sequenceM1, and can phase-correct the second MR data by using second averagedata near the time phase of the second collection sequence M2, and thuscan improve the accuracy of phase correction and improve image qualityof real images.

As a modification of the present embodiment, it is possible to apply thefirst IR pulse IR1 and the first spoiler pulse Sp1 to the first regionRe1, and apply the second IR pulse IR2 and the second spoiler pulse Sp2to the second region Re2, as in the first embodiment. As a furthermodification of the present embodiment, multiband imaging may be appliedas in the application of the first embodiment. The processing andadvantages of those modifications are the same as those of the firstembodiment and the application of the first embodiment, and descriptionsthereof will be omitted.

Third Embodiment

The third embodiment differs from the first embodiment, the application,and the second embodiment in that collection of MR data and collectionof reference data are shifted for every cardiac cycle and slice as shownin FIG. 8. FIG. 8 is a diagram showing an example of the sequences ofthe PSIR method executed in the present embodiment. (a) in FIG. 8 showsan electrocardiographic waveform of the subject P obtained by anelectrocardiograph. (b) in FIG. 8 shows the timing of application of thefirst IR pulse IR1 and the second IR pulse IR2 to the subject P. (c) inFIG. 8 shows a temporal change of longitudinal magnetization Mz1 in thefirst slice SL1. (d) in FIG. 8 shows a temporal change of longitudinalmagnetization Mz2 in the second slice SL2. (e) in FIG. 8 shows atemporal change of longitudinal magnetization Mz3 in a third slice apartfrom the first slice SL1 and the second slice SL2.

As shown in FIG. 8, the first sequence S1 includes a first IR pulse IR1,a first collection sequence M1, and a first spoiler pulse Sp1. Thesecond sequence S2 includes a second IR pulse IR2, a second collectionsequence M2, a second spoiler pulse Sp2, and a first referencecollection sequence R1. The third sequence S3 includes a third IR pulseIR3, a third collection sequence M3, a third spoiler pulse Spa, and asecond reference collection sequence R2. The fourth sequence S4 includesa third reference collection sequence R3.

Descriptions will be provided assuming that the number of slices to beimaged in the present embodiment is three as shown in FIG. 8; however,the number of slices is not limited to this number. The first IR pulseIR1 and the first spoiler pulse Sp1 in the present embodiment areselectively applied to the first slice SL1 as in the second embodiment.The second IR pulse IR2 and the second spoiler pulse Sp2 in the presentembodiment are selectively applied to the second slice SL2 as in thesecond embodiment.

The third IR pulse IR3 is an RF pulse that inverts nuclear magnetizationin the third slice. The third IR pulse IR3 is selectively applied to thethird slice at time t₃, which is the predetermined time after an R wavein a third cardiac cycle CC3.

The third collection sequence M3 is a sequence for collecting MR datafor an image relating to the third slice (hereinafter referred to asthird MR data) after application of the third IR pulse IR3 in the thirdcardiac cycle CC3. The third collection sequence M3 is the same as thefirst and second collection sequences M1 and M2 other than the cardiaccycle and the slice position.

The third spoiler pulse Sp3 is a spoiler pulse that recovers nuclearmagnetization in the third slice. After execution of the thirdcollection sequence M3 in the third cardiac cycle CC3, the third spoilerpulse Sp3 is selectively applied to the third slice. The third spoilerpulse Sp3 is the same as the first spoiler pulse Sp1 and the secondspoiler pulse Sp2 other than the cardiac cycle and the applicationregion.

The first to third reference collection sequences R1, R2, and R3 in thepresent embodiment are executed by using a second flip angle that isequal to or larger than the flip angle in the first and secondcollection sequences M1 and M2 (hereinafter referred to as a first flipangle). For example, the second flip angle used in the first to thirdreference collection sequences R1, R2, and R3 is set to be larger thanthe flip angle in the first and second reference collection sequences inthe first embodiment and the second embodiment. The first flip angle isstored in the storage apparatus 129 together with the first to thirdsequences S1, S2, and S3, and the second flip angle is stored in thestorage apparatus 129 together with the second to fourth sequences S2,S3, and S4.

The second reference collection sequence R2 is a sequence for collectingsecond reference data from the second slice after application of thethird spoiler pulse Spa in the third cardiac cycle CC3. The secondreference collection sequence R2 is the same as the first referencecollection sequence R1 other than the cardiac cycle and the sliceposition.

The third reference collection sequence R3 is a sequence for collectingreference data from the third slice (hereinafter referred to as thirdreference data) by using the second flip angle, in a cardiac phase of afourth cardiac cycle CC4, which is subsequent to the third cardiac cycleCC3, immediately after application of the spoiler pulses (the first tothird spoiler pulses). The third reference data is used for phasecorrection of the third MR data. The third reference collection sequenceR3 is the same as the first and second reference collection sequences R1and R2 other than the cardiac cycle and the slice position.

(Operation)

The steps of the operation in the present embodiment will be describedwith reference to FIGS. 8 and 9. FIG. 9 is a diagram showing an exampleof the steps of the operation in the present embodiment. In thedescription of the operation, the processing different from that in thefirst embodiment will be described.

(Step Sc1)

The sequence control circuitry 121 executes the first sequence S1 in thefirst cardiac cycle CC1 to collect first MR data by using the first flipangle after application of the first IR pulse IR1 to the first sliceSL1. The sequence control circuitry 121 outputs the first MR data to theprocessing circuitry 131.

(Step Sc2)

The sequence control circuitry 121 executes the second sequence S2 inthe second cardiac cycle CC2 to collect second MR data by using thefirst flip angle, and to collect first reference data by using thesecond flip angle that is larger than the first flip angle. The sequencecontrol circuitry 121 outputs the second MR data and the first referencedata to the processing circuitry 131.

(Step Sc3)

The sequence control circuitry 121 executes the third sequence S3 in thethird cardiac cycle CC3 to collect third MR data by using the first flipangle, and to collect second reference data by using the second flipangle. Specifically, as shown in FIG. 8, the sequence control circuitry121 controls the transmission circuitry 113 to apply the third IR pulseIR3 to the third slice at time t₃, which is the predetermined time afterthe detection time of the first R wave in the third cardiac cycle CC3(or the last R wave in the second cardiac cycle CC2).

As shown in (d) of FIG. 8, the sequence control circuitry 121 executesthe third collection sequence M3 in an approximate diastolic phase ofthe third cardiac cycle CC3, and collects third MR data on the thirdslice. After collection of the third MR data, the sequence controlcircuitry 121 controls the transmission circuitry 113 and/or thegradient magnetic field power supply 105 to apply the third spoilerpulse Sp3 to the third slice. After application of the third spoilerpulse Sp3, the sequence control circuitry 121 executes the secondreference collection sequence R2, and collects second reference data.The sequence control circuitry 121 outputs the third MR data and thesecond reference data to the processing circuitry 131.

(Step Sc4)

The sequence control circuitry 121 executes the fourth sequence S4 inthe fourth cardiac cycle CC4 to collect third reference data by usingthe second flip angle. Specifically, the sequence control circuitry 121executes the third reference collection sequence R3 in a cardiac phaseof the fourth cardiac cycle CC4 immediately after application of thefirst to third spoiler pulses (Sp1, Sp2, and Sp3), and collects thirdreference data. The sequence control circuitry 121 outputs the thirdreference data to the processing circuitry 131.

With the image generation function 1313, the processing circuitry 131performs the processing from step Sa3 to step Sa6 in FIG. 3 on each ofthe first slice SL1, the second slice SL2, and the third slice, andgenerates a real image of the first slice SL1, the second slice SL2, andthe third slice.

The processing from step Sc1 to step Sc4 and processing for generating areal image of each slice may be repeated as appropriate. At this time,the fourth sequence S4 may be incorporated into the first sequence S1.The processing from step Sc1 to step Sc4 and processing for generating areal image of each slice may be repeated as appropriate until aplurality of real images corresponding to a plurality of slices requiredby the operator can be obtained at the imaging target site. At thistime, an IR pulse, collection sequence, and spoiler pulse relating to aslice different from the first to third slices may be incorporated intothe fourth sequence S4.

The above-described configuration has the following advantages:

The MRI apparatus 100 according to the present embodiment can execute,in a first cardiac cycle CC1, a first sequence S1 for applying a firstIR pulse IR1 to a first slice SL1, collecting first MR data on the firstslice SL1 by using a first flip angle after application of the first IRpulse IR1, and applying a first spoiler pulse Sp1 to the first slice SL1after collection of the first MR data. The present MRI apparatus 100 canalso execute, in a second cardiac cycle CC2, a second sequence S2 forapplying a second IR pulse IR2 to a second slice SL2, collecting secondMR data by using the first flip angle after application of the second IRpulse IR2, applying a second spoiler pulse Sp2 to the second slice SL2after collection of the second MR data, and collecting first referencedata by using a second flip angle after application of the secondspoiler pulse Sp2. Furthermore, the present MRI apparatus 100 canexecute, in a third cardiac cycle CC3, a third sequence S3 for applyinga third IR pulse IR3 to a third slice, collecting third MR data by usingthe first flip angle after application of the third IR pulse IR3,applying a third spoiler pulse Sp3 to the third slice after collectionof the third MR data, and collecting second reference data by using thesecond flip angle after application of the third spoiler pulse Sp3.Moreover, the present MRI apparatus 100 can execute a fourth sequence S4for collecting third reference data by using the second flip angle, in acardiac phase of the fourth cardiac cycle CC4 immediately afterapplication of the third spoiler pulse Sp3.

As described above, the MRI apparatus 100 in the present embodiment canreduce the imaging time in imaging by the PSIR method. In addition,according to the present MRI apparatus 100, when the processing fromstep Sc1 to step Sc4 and processing for generating a real image of eachslice are repeated, a time interval corresponding to approximately oneheartbeat can be provided between an MR data collection sequence and areference collection sequence for each slice. Consequently, longitudinalmagnetization immediately after execution of a reference collectionsequence can be recovered to regain the thermal equilibrium state.Therefore, the present MRI apparatus 100 can collect the first to thirdreference data by using a second flip angle that is equal to or largerthan the first flip angle, for example, a second flip angle larger thanthe flip angle in the first and second embodiments, in the first tothird reference collection sequences R1, R2, and R3. The SNR of an MRimage is larger when the flip angle is larger. Therefore, the MRIapparatus 100 of the present embodiment can improve the SNR of the firstto third phase correction data used for phase correction. Accordinglythe present MRI apparatus 100 can improve the accuracy of phasecorrection and improve the image quality of real images.

As a modification of the present embodiment, it is possible to apply thefirst IR pulse IR1 and the first spoiler pulse Sp1 to the first regionRe1, apply the second IR pulse IR2 and the second spoiler pulse Sp2 tothe second region Re2, and apply the third IR pulse IR3 and the thirdspoiler pulse Sp3 to a third region different from the first region Re1and the second region Re2 and including the third slice, as in the firstembodiment. In addition, when four slices are to be imaged, of theregions respectively including the slices, two regions sandwichinganother region therebetween may be sequentially applied with an IR pulseto collect MR data, to avoid interference between IR pulses applied toadjacent regions. As a further modification of the present embodiment,multiband imaging may be applied to the present embodiment as in themodification of the first embodiment.

As a further modification of the present embodiment, it is possible tofurther collect first reference data from the first slice SL1immediately before collection of second MR data, further collect secondreference data from the second slice SL2 immediately before collectionof third MR data, and further collect third reference data from thethird slice in a cardiac phase of the fourth cardiac cycle CC4immediately before collection of the third MR data, as in the secondembodiment. The processing and advantages of those modifications are thesame as those of the first embodiment, the application of the firstembodiment, and the second embodiment, and descriptions thereof will beomitted.

As a modification of the first and second embodiments, a spoiler pulsemay be applied immediately after a reference collection sequence. Inthis case, in any of the embodiments and modifications and the like, itis possible to make the second flip angle equal to or larger than thefirst flip angle, and to improve the accuracy of phase correction andimprove the image quality of real images.

The MRI apparatus 100 in the embodiments and at least one modificationor the like as described above can reduce the imaging time in imaging bythe PSIR method.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1. A magnetic resonance imaging apparatus, comprising: sequence controlcircuitry that collects first MR data in a first cardiac cycle byexcitation of a first region including a first slice, and collectsreference data used for phase correction of second MR data on a secondslice not included in the first region before and after collection ofthe first MR data in the first cardiac cycle.
 2. The magnetic resonanceimaging apparatus according to claim 1, wherein the sequence controlcircuitry collects the second MR data in a second cardiac cycle that isdifferent from the first cardiac cycle by excitation of a second regionincluding the second slice, and the magnetic resonance imaging apparatusfurther comprises processing circuitry that phase-corrects the second MRdata obtained in the second cardiac cycle by using the reference data.3. The magnetic resonance imaging apparatus according to claim 1,wherein in the first cardiac cycle, the sequence control circuitryapplies an IR pulse to the first region before collection of thereference data, applies a recovery pulse for recovery of nuclearmagnetization to the first region after correction of the first MR data,and collects the reference data after application of the recovery pulse.4. The magnetic resonance imaging apparatus according to claim 1,wherein the first slice has a thickness corresponding to a plurality ofslices, the second slice has a thickness corresponding to a plurality ofslices, and the sequence control circuitry applies an RF pulse in amulti-frequency band corresponding to the first slice to the first slicewhen the first MR data is collected, and applies an RF pulse in amulti-frequency band corresponding to the second slice to the secondslice when the reference data is collected.
 5. The magnetic resonanceimaging apparatus according to claim 1, further comprising: processingcircuitry that generates average data by performing averaging processingon the reference data collected before and after collection of the firstMR data, and generates a real image by performing phase correction onthe first MR data by using the average data.
 6. A magnetic resonanceimaging method, comprising: collecting first MR data in a first cardiaccycle by excitation of a first region including a first slice and,collecting reference data used for phase correction of second MR data ona second slice not included in the first region before and aftercollection of the first MR data in the first cardiac cycle.
 7. Themagnetic resonance imaging method according to claim 6, furthercomprising: collecting the second MR data in a second cardiac cycle thatis different from the first cardiac cycle by excitation of a secondregion including the second slice, and phase-correcting the second MRdata obtained in the second cardiac cycle by using the reference data.8. The magnetic resonance imaging method according to claim 6, furthercomprising in the first cardiac cycle, applying an IR pulse to the firstregion before collection of the reference data, applying a recoverypulse for recovery of nuclear magnetization to the first region aftercorrection of the first MR data, and collecting the reference data afterapplication of the recovery pulse.
 9. The magnetic resonance imagingmethod according to claim 6, wherein the first slice has a thicknesscorresponding to a plurality of slices, the second slice has a thicknesscorresponding to a plurality of slices, and the magnetic resonanceimaging method further comprises: applying an RF pulse in amulti-frequency band corresponding to the first slice to the first slicewhen the first MR data is collected, and applying an RF pulse in amulti-frequency band corresponding to the second slice to the secondslice when the reference data is collected.
 10. The magnetic resonanceimaging method according to claim 6, further comprising generatingaverage data by performing averaging processing on the reference datacollected before and after collection of the first MR data, andgenerating a real image by performing phase correction on the first MRdata by using the average data.